CHICAGO (Reuters) - Drinking alcohol dulls the brain's
ability to detect threats, U.S. researchers said on Tuesday in
a study that helps explain why people who are drunk cannot tell
when the guy at the end of the bar is angling for a fight.

They said the study is the first to show how alcohol
affects the human brain as it responds to threats.

"You see this all of the time. People get into
confrontations when they are intoxicated that they probably
wouldn't get into when they are sober," said Jodi Gilman of the
National Institutes on Alcohol Abuse and Alcoholism, whose
study appears in the Journal of Neuroscience.

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Gilman studied 12 people who were given intravenous
infusions of alcohol and then monitored their brain activity
using functional magnetic resonance imaging while they looked
at pictures of frightened and neutral faces.

Her team did the same study on these people when they were
given a simple saline infusion as a placebo.

As expected, when people were given the placebo, their
brains responded to the fearful faces.

"Our brains respond more to fearful stimuli," Gilman said
in a telephone interview. "They signal to us that we are in
threatening situations."

When these same people were given infusions of alcohol,
however, this response was dulled, suggesting that while
intoxicated, "our brain can't distinguish between the
threatening and nonthreatening stimuli," said Gilman.

She said this impaired appreciation for threats could lead
to a host of risky situations, including drunk driving. And it
also explains why alcohol is sometimes called a social
lubricant.

"People have used alcohol for years to become euphoric and
to decrease anxiety. Alcohol has been used in particular to
increase sociability. How alcohol acts on the brain to produce
these effects has not been well understood or studied," Gilman
said.

Her study found that alcohol increases activity in a reward
center of the brain known as the striatum. And they found a
link between the level of activation in this region and how
intoxicated people said they were feeling, which could help
account for the addictive properties of alcohol.

"This is important because we think we can develop
potential treatments for alcoholism," Gilman said.

People in the study were social drinkers, not heavy
drinkers. Gilman said the research team plans to conduct the
study in heavy drinkers next.